1. Field of the Invention
This invention relates to the extraction of geothermal heat energy from the earth and its utilization of the earth's surface. More particularly, this invention is a part of the technical aspects of stimulating the flow of geothermal wells for the recovery of heat carried therein and the conversion of this heat to electrical energy.
It is known that the interior of the earth is a molten mass of rock and is very hot. Water in contact with the hot interior of the earth is termed geothermal fluid. This geothermal fluid contains heat energy that may advantageously and effectively be used as a source of energy for the generation of power or in other heat recovery schemes. The geothermal fluid may be steam released from volcanic areas or hot water which is present in volcanic and in deep alluvial deposits that are porous enough to permit percolation of the water to the deep hot zones. This water may have a temperature as high as 700.degree. F. at a depth of 5,000 feet.
To lift the water from the depth of the geothermal well to the well head where the heat therein can be utilized, a primary fluid is injected into the well under the surface of the water therein and with the action of the vaporized primary fluid, the geothermal water is lifted to the well head. Regulating the flow of the primary fluid into the well and starting up the well flow, continuously producing geothermal heat, converting this heat to electrical power and minimizing precipitation of solids in the well casing and other aspects of geothermal heat production are discussed herein.
2. Description of Prior Art
In some areas, the heat energy within the earth is carried to the surface by steam. This steam may be used directly in turbines to drive electrical generators.
The fluid from a geothermal well may flow naturally to the surface or may have to be pumped to the surface. Where pumping is required, it is typically accomplished by locating the pump at a selected level below the surface of the earth. When the pump is located in the well, a long drive shaft is generally required between the pump and the drive motor. Other geothermal well pumping devices have been proposed, including the electrically-driven pump where the motor and the pump are submersed in the well.
Many self-flowing water-dominated geothermal wells do not spontaneously flow without some startup stimulation. In the past, well startup stimulation was accomplished mainly by one of the following three methods:
a. By pumping fresh water down the well; PA1 b. By inserting a tube down the well and pumping air or inert gases down the tube; PA1 c. By inserting a tube down the well and pumping liquefied gases, such as liquid nitrogen or carbon dioxide down the tube.
In each case, the principle of the well startup is the same, namely a reduction in the density of the well fluid present in the well casing to cause disequilibrium in the well hydraulic system and thus commence the flow. Once started, the self-flowing well will continue to flow without any additional stimulation.
In an analagous system, the oil industry lifts much of its crude oil from the depth of the well by means of gas lifting. In artificial gas lifting, compressed natural gas is introduced down the well through valves that control the flow and the quantity of gas introduced. The natural gas thereafter lifts the oil up the casing and to the surface where the gas is disengaged from the oil and recycled back to produce additional oil. This system of oil lift has been in operation for many years.
There are a number of processing systems devised for the conversion of geothermal heat into electrical power. Some of them utilize an organic liquid as the working fluid and others utilize the geothermal steam itself or the combined geothermal steam and brine to produce electrical power. Each specific system may be advantageous under some set of circumstances with the proper type of geothermal resource. The power production processing systems mentioned above rely either on geothermal heat production from self-flowing geothermal wells or on mechanical lifting of geothermal brine to the well head.
The building up of scale in the geothermal well casing has been known for many years. The causes of the scale buildup and the methods of preventing scale buildup are well understood. One proposed system of preventing scale buildup in the well casing is to mechanically lift the geothermal brine and thus eliminate steam flashing in the well casing. To date, the art of mechanically pumping geothermal wells has not been reduced to practice. The physical conditions inside a geothermal well casing are hostile to the delicate moving or rotating machinery. The pressure of non-condensible gases, together with the geothermal liquid, makes conventional pumping of geothermal liquids more difficult.